1. Field of the Invention
The present invention relates to a mold assembly suitable for making a multilayer molded article and a method of making the multilayer molded article using the same.
2. Related Background Art
Methods for making a thermoplastic resin molded article having protrusions such as ribs and bosses on its rear face by means of injection molding technique, injection compression molding technique, or the like have conventionally been well-known. In the thermoplastic resin molded article manufactured by such a method, a sink is likely to occur at a position on its base material surface corresponding to a protrusion, thereby making it difficult to yield a smooth surface.
Known as means for overcoming such a problem is a molding method using a foaming agent. In this method, however, it is difficult to control the state of foaming. Also, even in this method, a molded article having a smooth surface without sinks is hard to obtain. Further, the foaming agent is expensive in general, and its thermal stability upon heating may not be sufficient.
Known as another means is a method in which, from the viewpoint of form, the thickness of a protrusion such as rib or boss is made smaller than that of the base material in contact therewith, thereby preventing sinks from occurring. In this method, however, the form may lack adaptability. Also, since its strength decreases, the thickness of the base material surface has to be increased in order to maintain the strength. Therefore, this method is greatly restricted in terms of form and is hard to respond to the recent tendency of the molded article toward lighter weight and smaller thickness.